1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording used for recording data on a recording medium by means of a perpendicular magnetic recording system, and to a head gimbal assembly, a head arm assembly, and a magnetic disk drive each of which incorporates the magnetic head for perpendicular magnetic recording.
2. Description of the Related Art
The recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in the direction orthogonal to the surface of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, compared with the longitudinal magnetic recording system.
It is known that there are types of magnetic heads for perpendicular magnetic recording one of which is a single-pole head and another one of which is a shield-type head. The single-pole head comprises: a medium facing surface that faces toward a recording medium; a coil for generating a magnetic field corresponding to data to be written on the recording medium; a pole layer (main pole) having an end face located in the medium facing surface, allowing a magnetic flux corresponding to the field generated by the coil to pass therethrough, and generating a write magnetic field for writing the data on the recording medium by means of the perpendicular magnetic recording system; an auxiliary pole having an end face located in the medium facing surface and having a portion that is located away from the medium facing surface and coupled to the pole layer; and a gap layer made of a nonmagnetic material and provided between the pole layer and the auxiliary pole. In the medium facing surface the end face of the auxiliary pole is located backward or forward of the end face of the pole layer along the direction of travel of the recording medium. The auxiliary pole has a function of returning a magnetic flux that has been generated from the end face of the pole layer and has magnetized the recording medium.
The shield-type head comprises: a medium facing surface that faces toward a recording medium; a coil for generating a magnetic field corresponding to data to be written on the recording medium; a pole layer having an end face located in the medium facing surface, allowing a magnetic flux corresponding to the field generated by the coil to pass therethrough, and generating a write magnetic field for writing the data on the recording medium by means of the perpendicular magnetic recording system; a write shield layer having an end face located in the medium facing surface and having a portion that is located away from the medium facing surface and coupled to the pole layer; and a gap layer made of a nonmagnetic material and provided between the pole layer and the write shield layer. In the medium facing surface the end face of the write shield layer is located forward of the end face of the pole layer along the direction of travel of the recording medium with a specific small space created by the thickness of the gap layer. The end face of the write shield layer has a width greater than that of the end face of the pole layer. The end face of the write shield layer has an area greater than that of the end face of the pole layer. In the shield-type head the write shield layer is capable of making the magnetic field gradient abrupt by taking in the magnetic flux generated from the pole layer. As a result, the shield-type head is capable of further improving the linear recording density. The magnetic field gradient means an amount of change of components orthogonal to the surface of the recording medium among components of the magnetic field generated from the pole layer, the amount of change being taken per unit length along the direction of travel of the recording medium. The write shield layer also has a function of returning a magnetic flux that has been generated from the end face of the pole layer and has magnetized the recording medium.
In each of the single-pole head and the shield-type head, the pole layer incorporates a track width defining portion and a wide portion, for example. The track width defining portion has an end located in the medium facing surface, and defines the track width. The wide portion is coupled to the other end of the track width defining portion and has a width greater than the width of the track width defining portion. The width of the track width defining portion is nearly uniform. For example, the wide portion is equal in width to the track width defining portion at the interface with the track width defining portion, and gradually increases in width as the distance from the medium facing surface increases and then maintains a specific width to the end of the wide portion.
For the magnetic head to achieve higher recording density, particularly required are a reduction in track width, that is, a reduction in width of the end face of the pole layer located in the medium facing surface, and an improvement in write characteristics. However, if the track width is reduced, write characteristics such as an overwrite property that is a parameter indicating an overwriting capability are degraded. Therefore, it is required to achieve better write characteristics as the track width is reduced.
In a magnetic head for perpendicular magnetic recording, it is known that there sometimes occurs a phenomenon in which data stored on a recording medium is erased by a magnetic field produced by the pole layer due to remanent magnetization of the pole layer when writing is not performed. The phenomenon will be hereinafter called pole erase.
Techniques for suppressing an occurrence of pole erase are known, such as those disclosed in Japanese Published Patent Application (hereinafter referred to as ‘JP-A’) 2005-38535, JP-A 2005-174449, and JP-A 2004-281023.
Each of JP-A 2005-38535 and JP-A 2005-174449 discloses a technique in which a write pole film (a pole layer) includes a soft magnetic film and a magnetic bias film, and an occurrence of pole erase is suppressed by directing the magnetization of the soft magnetic film to the direction of track width by means of the magnetic bias film.
JP-A 2004-281023 discloses a technique in which a main pole (a pole layer) incorporates a multilayer magnetic film made up of high saturation flux density layers and low saturation flux density layers, and an occurrence of pole erase is suppressed by making the direction of magnetization of a pair of high saturation flux density layers antiparallel, the high saturation flux density layers being opposed to each other with one of the low saturation flux density layers disposed in between.
U.S. Pat. No. 6,628,478 B2 discloses a technique in which, in a magnetic head for a longitudinal magnetic recording system, each of first and second pole layers opposed to each other with a gap layer disposed in between is formed of a mutilayer film made up of ferromagnetic films and nonmagnetic metal films, and a pair of ferromagnetic films adjacent to each other with one of the nonmagnetic metal films disposed in between are antiferromagnetically coupled to each other. This technique reduces the number of magnetic domain walls in each of the pole layers, and improves the high frequency response of the magnetic head.
A fact that a great remanent magnetic field is created in a portion of a pole layer is disclosed in Y Zhou et al., ‘POLE-TIP SIZE EFFECT ON PERPENDICULAR RECORDING HEAD REMANENCE’, Digests of Intermag 2005, DB04, 2005.
A problem that the structure of the pole layer is complicated is found in each of the techniques disclosed in JP-A 2005-38535, JP-A 2005-174449, JP-A 2004-281023, and U.S. Pat. No. 6,628,478 B2.
According to the techniques disclosed in JP-A 2005-38535 and JP-A 2005-174449, since the pole layer includes the soft magnetic film and the magnetic bias film, the number of steps required for manufacturing the magnetic head is increased, and a variety of materials are required for the magnetic head. As a result, these techniques have problems of an increase in costs for manufacturing the magnetic head and a reduction in throughput.
According to the techniques disclosed in JP-A 2004-281023 and U.S. Pat. No. 6,628,478 B2, currently-available methods of forming the pole layer are limited to physical vapor deposition such as sputtering. Consequently, these techniques have problems that the manufacturing process of the magnetic head is complicated and that the yield of the magnetic head is thereby reduced.
The inventors of the present patent application have found that the state of magnetization in the end face of the pole layer when writing is not performed relates to pole erase. The paper of Zhou et al. mentioned above does not address the relationship between the state of magnetization in the end face of the pole layer when writing is not performed and pole erase.